Sound In Thrillers:

Sound in thrillers is so important, not just sound effects but music most of all. Can you imagine the 'Shower Scene' in Alfred Hitchcock's 'Psycho' without any music? It wouldnt have half of the shock or mood it did with the music, it would just look like footage of a pretty woman taking a shower.

The same goes for the opening of 'Ronin' directed by John Frankenheimer. For the first five minutes or so nothing at all happens apart from one of the main characters walks down a flight of stairs and into a seedy bar. With the help of the tense music though you spend the entire scene on the edge of your seat waiting for something to happen just becuase the music suggests so. to help you understand this, here is the clip for that scene:

Sound Effects are equally as important as the soundtrack for thrillers. If the story requires a gun shot sound, what sort of gunshot sound do you need? A silenced gun sound is more mysterious and implies a secretive killing, however if you were to use a unsuppressed weapon sound in the same situation whilst it might shock the viewer more it could potentally ruin the stealthy moment of a film.